Global myocardial index (GMI) is a sensitive echocardiographic indicator of overall cardiac function. The aim of this study was to compare the GMI changes induced by Bi-V pacing to the variations in clinical, electrocardiographic and echocardiographic parameters currently used for evaluation of ventricular resynchronization in order to test the potential marker of positive clinical response.
Patients and methods: This study included 35 consecutive patients (pts), aged 65.7+/-7.5 years, implanted with an endocavitary Bi-V pacemaker for drug refractory severe heart failure. NYHA class was evaluated before implantation and at day 30. QRS duration (QRSd), echocardiographic interventricular delay (IVD), and GMI were determined in the paced and non-paced situation at day 1, 7 and 30 after implantation.
Results: NYHA class improved from 3.5+/-0.3 to 2.4+/-0.4 (p<0.01). GMI improved significantly (p<0.0001) after Bi-V in all pts from 1.25 +/- 0.5 to 0.77 +/- 0.34 and remained stable all along the study. GMI decrease (dGMI) in pts with NYHA functional class improvement > 0.5 was 0.52 +/- 0.16while dGMI in pts with NYHA functional class improvement < or = 0.5 was 0.21+/- 0.19. dGMI was statistically correlated with IVD shortening (r=0.67, p<0.0001) but not with QRSd shortening.
Conclusion: The GMI improves during Bi-V pacing, mostly in responders pts and the improvement remains unchanged after the implant. The GMI decrease induced by Bi-V pacing is correlated with the IVD shortening and NYHA functional class improvement.